core/log: copy early logs with sendfile/readwrite again

copy_file_range does not work across devices and memfds count as a
separate device.

src/core/logging.cpp

@@ -27,7 +27,10 @@
 #include <qtmetamacros.h>
 #include <qtypes.h>
 #include <sys/mman.h>
-#include <unistd.h>
+#ifdef __linux__
+#include <sys/sendfile.h>
+#include <sys/types.h>
+#endif
 
 #include "instanceinfo.hpp"
 #include "logcat.hpp"
@@ -43,6 +46,57 @@ using namespace qt_logging_registry;
 
 QS_LOGGING_CATEGORY(logLogging, "quickshell.logging", QtWarningMsg);
 
+namespace {
+bool copyFileData(int sourceFd, int destFd, qint64 size) {
+	auto usize = static_cast<size_t>(size);
+
+#ifdef __linux__
+	off_t offset = 0;
+	auto remaining = usize;
+
+	while (remaining > 0) {
+		auto r = sendfile(destFd, sourceFd, &offset, remaining);
+		if (r == -1) {
+			if (errno == EINTR) continue;
+			return false;
+		}
+		if (r == 0) break;
+		remaining -= static_cast<size_t>(r);
+	}
+
+	return true;
+#else
+	std::array<char, 64 * 1024> buffer = {};
+	auto remaining = totalTarget;
+
+	while (remaining > 0) {
+		auto chunk = std::min(remaining, buffer.size());
+		auto r = ::read(sourceFd, buffer.data(), chunk);
+		if (r == -1) {
+			if (errno == EINTR) continue;
+			return false;
+		}
+		if (r == 0) break;
+
+		auto readBytes = static_cast<size_t>(r);
+		size_t written = 0;
+		while (written < readBytes) {
+			auto w = ::write(destFd, buffer.data() + written, readBytes - written);
+			if (w == -1) {
+				if (errno == EINTR) continue;
+				return false;
+			}
+			written += static_cast<size_t>(w);
+		}
+
+		remaining -= readBytes;
+	}
+
+	return true;
+#endif
+}
+} // namespace
+
 bool LogMessage::operator==(const LogMessage& other) const {
 	// note: not including time
 	return this->type == other.type && this->category == other.category && this->body == other.body;
@@ -414,7 +468,11 @@ void ThreadLogging::initFs() {
 		auto* oldFile = this->file;
 		if (oldFile) {
 			oldFile->seek(0);
-			copy_file_range(oldFile->handle(), nullptr, file->handle(), nullptr, oldFile->size(), 0);
+
+			if (!copyFileData(oldFile->handle(), file->handle(), oldFile->size())) {
+				qCritical(logLogging) << "Failed to copy log from memfd with error code " << errno
+				                      << qt_error_string(errno);
+			}
 		}
 
 		this->file = file;
@@ -426,14 +484,10 @@ void ThreadLogging::initFs() {
 		auto* oldFile = this->detailedFile;
 		if (oldFile) {
 			oldFile->seek(0);
-			copy_file_range(
-			    oldFile->handle(),
-			    nullptr,
-			    detailedFile->handle(),
-			    nullptr,
-			    oldFile->size(),
-			    0
-			);
+			if (!copyFileData(oldFile->handle(), detailedFile->handle(), oldFile->size())) {
+				qCritical(logLogging) << "Failed to copy detailed log from memfd with error code " << errno
+				                      << qt_error_string(errno);
+			}
 		}
 
 		crash::CrashInfo::INSTANCE.logFd = detailedFile->handle();